Systems Manager Patching Maintenance Window with Cron

A company uses AWS Systems Manager Patch Manager to automate patching of Amazon EC2 instances. The SysOps administrator needs to configure a maintenance window that will patch instances on the second Tuesday of every month at 2:00 AM. The administrator wants to ensure that patches are automatically applied but reboots are only performed if required. Which combination of configurations should the administrator use?

Quick Answer

The correct combination is a maintenance window with the cron schedule `cron(0 2 ? * TUE#2 *)` paired with the `AWS-RunPatchBaseline` SSM document using operation `Install` and reboot option `RebootIfNeeded`. This cron expression specifically targets the second Tuesday of each month at 2:00 AM by using the `?` wildcard for day-of-week and `TUE#2` to denote the ordinal occurrence, while the `Install` operation applies all available patches and the `RebootIfNeeded` setting ensures the instance only reboots when a patch requires it, avoiding unnecessary downtime. On the SOA-C02 exam, this scenario tests your understanding of Systems Manager patching with maintenance windows and cron schedule syntax, a common trap being confusion between `TUE#2` and simpler day-of-month expressions like `15`—remember that `#` denotes ordinal weekdays. A helpful memory tip: think “TUE#2 = second Tuesday” and “RebootIfNeeded = reboot only when mandatory.”

⚠ Common exam trap

It's easy for candidates to confuse the cron syntax for 'second Tuesday' with simpler day-of-month or day-of-week expressions, or mistakenly use invalid SSM document names like `AWS-ApplyPatchBaseline` or `AWS-InstallPatchBaseline`, which do not exist in AWS Systems Manager.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Create a maintenance window with a cron schedule of cron(0 2 ? * TUE#2 *) and use an AWS-RunPatchBaseline document with operation 'Install' and reboot option 'RebootIfNeeded'.

It uses the cron expression `cron(0 2 ? * TUE#2 *)` to schedule the maintenance window for the second Tuesday of every month at 2:00 AM, and the `AWS-RunPatchBaseline` document with operation `Install` and reboot option `RebootIfNeeded` ensures patches are applied automatically and reboots only occur when required by the patch installation.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✓
Create a maintenance window with a cron schedule of cron(0 2 ? * TUE#2 *) and use an AWS-RunPatchBaseline document with operation 'Install' and reboot option 'RebootIfNeeded'.
Why this is correct
This schedule correctly specifies the second Tuesday of each month at 2 AM. The document and operation apply patches, and RebootIfNeeded only reboots if necessary.
✗
Create a maintenance window with a rate schedule of 30 days and use an AWS-ApplyPatchBaseline document with operation 'Scan' and reboot option 'RebootIfNeeded'.
Why it's wrong here
A rate schedule cannot specify a particular day of the week. The operation 'Scan' only checks for missing patches without installing them.
✗
Create a maintenance window with a cron schedule of cron(0 2 14 * ? *) and use an AWS-RunPatchBaseline document with operation 'Install' and reboot option 'RebootIfNeeded'.
Why it's wrong here
This cron schedule triggers on the 14th day of every month, not the second Tuesday.
✗
Create a maintenance window with a cron schedule of cron(0 2 2 * 2 *) and use an AWS-InstallPatchBaseline document with operation 'Install' and reboot option 'NoReboot'.
Why it's wrong here
The cron expression is invalid; the correct format uses ? for day-of-week and * for month. Also, AWS-InstallPatchBaseline is not a valid SSM document.

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Same concept, more angles

2 more ways this is tested on SOA-C02

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A company uses AWS Systems Manager to automate patching of EC2 instances. The instances are in an Auto Scaling group. The company wants to ensure that patching does not affect application availability. Which feature should be used?

easy

A.State Manager
✓ B.Maintenance Windows
C.Patch Manager
D.Run Command

Why B: Systems Manager Maintenance Windows allow scheduling patching during specific time windows, and can be configured to work with Auto Scaling to maintain availability by ensuring instances are patched without affecting the overall application availability. Option A is wrong because State Manager is used for maintaining consistent configuration of instances, not for scheduling patching. Option C is wrong because Patch Manager is the service that applies patches, but it is typically run within a Maintenance Window to control timing and availability. Option D is wrong because Run Command is for executing ad-hoc commands and scripts, not for scheduled patching with availability considerations.

Variation 2. A company uses AWS Systems Manager to automate patching of EC2 instances. The SysOps administrator creates a Maintenance Window that targets a list of instances. The patching task fails with the error: 'Instance is not in a supported state.' What should the administrator check FIRST?

medium

A.Verify that the instance has a public IP address.
B.Verify that the instance's security group allows inbound traffic from Systems Manager.
✓ C.Verify that the SSM Agent is installed and running on the instance.
D.Verify that the instance has an IAM instance profile attached with the necessary permissions.

Why C: Systems Manager requires the SSM Agent to be installed and running on the instance to execute patching commands. Option A is incorrect because patching does not require a public IP address; instances can be in a private subnet with appropriate VPC endpoints. Option B is incorrect because the security group does not need to allow inbound traffic from Systems Manager; Systems Manager uses outbound traffic initiated by the SSM Agent. Option D is incorrect because while an IAM instance profile with appropriate permissions is necessary for Systems Manager, the error 'Instance is not in a supported state' specifically indicates that the SSM Agent is not installed or running, so the first thing to check is the agent status.

Last reviewed: Jun 11, 2026

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